1981 SuperSport Rebuild

[81SuperChris]

Hey CB750,
I've got an 81 Supersport that has a lot of little projects to facilitate me learning about engines - I'll keep all of my progress and problems here. Thanks to this community for existing! Here's the bike.



After getting it running thanks to a clymer and alot of reading + 1 or 2 posts here, the engine died on me.  It's given me some clues, and I'd love your experience in problem solving with me. I'll try and keep it short and sweet below.

I was losing power on my longest trip yet(45 mins). Since I've had it the idle speed has been all over the place, dying at any low RPM, needing lots of gas to stay alive. I noticed liquid leaking from 2nd exhaust(pictured). Bike fully died on my way back. After getting it home I pulled the plugs, exhaust, alternator and valve head cover off and this is what I found.

A little leak on the cover head


#2 Spark Plug had a corroded connection at the plug head and pulled off easily from the plug cable when working on it.

Black Exhaust Port #2 and Oil fouled #2 Spark Plug


Rust On Alternator



Valve Clearances:

 Intake           Exhaust
.1-.13     1     .05-.08
.1-.13     1     .08.-.1

.1-.13     2     .08-.1
.1-.13     2     .08

.1-.13     3     .1-.13
.1-.13     3     .1-.13

.13-.15   4     .15
.13-.15   4     .1


I'll preface all this by noting that I have 1 full overhaul gasket kit from vintage and a compression tester set. My main goal is to learn, but I want to be sure I'm checking, cleaning, or fixing the right things at the right times rather than gung ho break it all apart at once style.

My Current plan:
Fix the clearances to be within .08(or .05 if possible), check the valve head for cracks, reattach the sparkplug head, ensuring solid connection and reclean the carbs by soaking this time, and reseal all gaskets.

So here's my questions:

1) What does this problem sound like to you?

2) Is it worth it to go deeper and replace the valve seals and/or take the whole engine off now?

3) Could this be a timing issue and if so, should I wait until everything else is back together?

4) Cam chain adjustment perhaps?

5) What kind of good can I do for a slightly rusted alternator while its open? Rubbing alcohol maybe? It currently works.


I know theres a right priority to check and/or fix for this - I'd just like a plan of attack and some insight.

Let me know if there's any pics or further info you'd like in solving this. Thanks in advance everyone!

[TOOLS1]

1) What does this problem sound like to you? A vacuum leak. Most likely the boots between the carbs, and the head.

2) Is it worth it to go deeper and replace the valve seals and/or take the whole engine off now? No!

3) Could this be a timing issue and if so, should I wait until everything else is back together? Not likely, and yes,

4) Cam chain adjustment perhaps? Definitely!

5) What kind of good can I do for a slightly rusted alternator while its open? Rubbing alcohol maybe? It currently works. PB Blaster, and a scotchbrite pad, or fine steel wool.

TOOLS

[81SuperChris]

Thanks tools, I'm on it!

Because most of the shims need to be replaced by the same amount(from .1 down to .05), will buying a kit online(ie bikebandit) still work? Shims at the dealer cost 14$ a pop and I'd rather not blow 200 there.

[81SuperChris]

I've got some more clues for you tools!

I found white foam(?) in the air tube leading up to the air box from the oil pan. After taking off the carbs, the  carb to header boots were indeed loose and it is wet around the socket on the carb side. I think you're right about the vacuum leak.

What is this white foam?

[TOOLS1]

The foam is from moisture in the oil, and is common. I would talk to some more dealers about the shims. Sometimes they will exchange them for a small fee.
TOOLS

[motogrady]

headlights, brakelights, running lights are draining the battery,
killing it and your ride.

sounds like a charging issue, check by charging the battery real good and see how it runs then.
if the starter drags real bad when it dies, or is about to, well........it ain't lack of fuel or compression.

disconnect the headlight, running lights, don't use the horn, you might go 200 miles on a charge.

[81SuperChris]

You were completely right TOOLS - it was a vaccuum leak. Thank you, I rode by bike for a few days before a fork seal leak crept up on me. I'm trying to replace them, and now I have a new issue.

The fork seals are completely stuck in the forks, like they're glued in! I followed the intructions in my clymer in conjunction with ReRun's intructions, but got stopped when the bottom allen bolt was completely stuck. There was scoring on them before, but now I've totally stripped them out. I then tried simply heating up and pulling the seals out with a screwdriver, but the rubber is not budging. I've dug a bit out but there has to be another way - have you had this happen before?

Do I:

1) Drill out the allen bolts and pull the cover off to get at the seals

2) Use acid to break down whatever is holding the seal in

What would you do in this situation?

Should I go ahead and find a replacement for these old boys?

[TOOLS1]

I am confused here. If you could not get the alen bolt out of the bottom, how could you have removed the slider, and be removing the seal?
I would start with drilling the head off the alen bolt, and then the slider should come off the tube. Then you can place a nut over the piece of alen bolt that is left in, and weld the nut to it. Then just screw it out. Replace it with a new bolt.
TOOLS

[81SuperChris]

Hi tools, we drilled out the nuts - I learned my lesson to ALWAYS use an impact wrench for stuck bolts. It's now on my wish list.

Now I've gone to the honda dealer here and he's given me some odd bolts to try and get me riding before the real ones come in. The black one is the stripped one, the shiny ones are the temporary replacements.

1) Can I get away with these bolts if the head of them doesn't interfere with the wheel?

2) Will the extra length alter/hurt the performance of the forks?

3) Does it matter that the midsection is threaded and not bare?

My plan now is to try the new bolts and shave them down as necessary to make them fit. If anyone thinks this is a bad idea, please let me know.

Cheers,
Chris

[TOOLS1]

1) Can I get away with these bolts if the head of them doesn't interfere with the wheel? Yes!

2) Will the extra length alter/hurt the performance of the forks? No!

3) Does it matter that the midsection is threaded and not bare? No!

Those should work just fine. Just be sure to put a copper crush washer on them. If you do not have the old ones, you can get them at any autoparts store in the brake section.
TOOLS

[81SuperChris]

These fit perfectly and I'm so so happy you agree! THANK YOU!

[81SuperChris]

Also, I'm applying a little gasket sealer on the cover like you said. But do you cover all parts below the seal with a light coat of ATF oil?

[81SuperChris]

And - sorry for all the questions - the beveled edge goes up on the seal? You other post on this wasn't clear enough for me.

** As in the circular line DOWN, beveled edge up **

[TOOLS1]

If you can see a tiny spring in the seal, that side definitely goes down, or to the inside. If not you put the side with the deepest ridge to the inside. Usually markings go to the outside.
TOOLS